Bredt olefins protonation

The structures of regioisomers, represented by the partial formulas 77 and 78 and formed by addition of organic azides to Bredt olefins, can be assigned unambiguously by lH- and 13C-NMR spectra. In structure 77 the proton a to the N=N double bond appears at lower field than the proton a to the /V-Ph group with approximately AS = 0.8 ppm. In the13C-NMR spectra a chemical... 

Ormojanine (CLXIV) behaves analogously to panamine toward sodium borohydride. The NMR-spectrum of it evidences an olefinic proton and the Hofmann degradation product (CLXV) generates a diene which indicates 2 olefinic protons. The position of the double bond in CLXV violates the Bredt rule but the presumption is that the rule does not necessarily apply to rings of such size. 

For the hydronium-ion-catalyzed hydration of bicyclo[4.2.1]non-l-ene (177) and bicyclo[4.2.1]non-l(8)-ene (176), appreciable solvent isotope effects have been observed. Since these correspond to those found for reactions of unstrained olefins, it was concluded that the hydration proceeds as with unstrained alkenes by a two-step mechanism protonation of the double bond is followed by addition of the nucleophile (152b). The strained olefin with its distorted double bond is higher in energy and more reactive than an unstrained alkene. Hence, the transition state for protonation of Bredt-olefins is expected to be an early one (95). 

The rates of hydration of the Bredt-olefins 69 and 176 (Table 27) have been used to estimate strain effects in electrophilic reactions of these strained olefins. It was estimated that the 105-fold rate increase of 69 over 2-methyl-but-2-ene (257a) is due to about 50% strain release in the transition state of protonation. 

Bredt s amides are very reactive Twisted amides display enhanced sensitivity to hydrolysis and a host of other interesting chemical peccadillos. For example, Kirby reported the formation of stable tetrahedral intermediates from l-aza-2-adamantanone (Figure 11.56). This compound combines amine reactivity (it can be rapidly protonated) with ketone reactivity (it undergoes Wittig olefination). ... 

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